High temperature fuel cell generators employing interconnected, tubular fuel cells, with solid electrolytes, are taught by A. O. Isenberg, in U.S. Pat. No. 4,395,468. Fuel electrode, air electrode, solid electrolyte and interconnection configurations for individual fuel cells are taught by A. O. Isenberg, in U.S. Ser. No. 323,641, now U.S. Pat. No. 4,490,444 filed on Nov. 20, 1981. Usually, a porous support tube of calcia stabilized zirconia, approximately 1 millimeter to 2 millimeters thick, has an air electrode deposited on it. The air electrode is from about 50 microns to 1000 microns thick (0.05 millimeter to 1 millimeter) and may be made of, for example, LaMnO.sub.3, CaMnO.sub.3, LaNiO.sub.3, LaCoO.sub.3, LaCrO.sub.3, etc. Surrounding the outer periphery of the air electrode is a layer of gas-tight solid electrolyte, usually yttria stabilized zirconia, approximately 1 micron to 100 microns (0.001 millimeter to 0.1 millimeter) thick. A selected radial segment of the air electrode is covered by an interconnect material. The interconnect material may be made of a doped lanthanum chromite film, of approximately 50 microns (0.05 millimeter) thickness. The lanthanum chromite is doped with calcium, strontium, or magnesium.
Both the electrolyte and interconnect material are applied on top of the air electrode by a modified chemical vapor deposition process, employing the use of vaporized halides of zirconium or yttrium for the electrolyte, or of calcium, magnesium, lanthanum, or the like, for the interconnect material, at temperatures of up to 1450.degree. C. Such halide vapors can interact with and degrade the air electrode material during the initial period of electrolyte and interconnect application. This causes, in some instances, air electrode leaching of dopants, such as strontium, or leaching of main constituents, such as lanthanum or manganese. Such leaching causes a resultant, deleterious alteration of electrical, chemical, and mechanical properties of the air electrode, due to substantial modification at the electrolyte interface. Additionally, even after electrolyte application, there may be long term diffusion of manganese from the air electrode into the electrolyte during operation of the electrochemical cell. There is a need then for some means to protect the air electrode from highly reactive chlorine or other halide vapors during deposition of the electrolyte and interconnect layers, and over the long term operations of the cell.